Purification of titanium



Unitid S Patent PURIFICATION OF TITANIUM Leo Goldenberg, Prince Georges County, Md. (900 Malta Lane, Silver Spring, Md.)

No Drawing. Filed Sept. 14, 1954, Ser. No. 456,057 3 Claims. (Cl. 204-64) This invention relates to a process for purifying metallie titanium, more specifically it relates to an electrolytic process for reducing the oxygen content of titanium metal.

In copending application S.N. 414,899 now Patent No. 2,881,119 there has been disclosed a process for elect roplating titanium from a fused salt electrolyte. An 1mportant characteristic of this process is its use of a soluble anode made of titanium. Although substantially oxygenfree titanium is commercially available, it is available only at a relatively high price, whereas oxygencontaminated titanium, being unsuitable for many structural uses, commands a much lower scrap price. Over and above the present state of the art in terms of commercial availability, there are several known pyrometallurgical processes capable of partially reducing titanium dioxide to the metal. However, these processes are presently incapable of reducing the oxygen content to the low level of beneath /z% which is required for commercially satisfactory titanium metal.

Accordingly the prime object of the present invention is to provide a process for reducing the oxygen content of oxygen-contaminated titanium metal, i.e. metal containing more than /2 oxygen.

Further objects and advantages will appear from the description of the invention which follows.

Briefly stated, this invention comprises the anodic solution of an oxygen-contaminated titanium into a fused salt electrolyte with a cathodic deposition of titanium metal having a lesser oxygen content than the starting material. The decrease of oxygen content is effected by deoxygenating the electrolyte; that is to say by the positive removal of dissolved oxygen from the electrolyte, over and above the deoxygenation process inherent in the plating process per se. Tests using an electrolytic cell of fused magnesium chloride as the electrolyte, and oxygen-contaminated titanium anodes, resulted in a carryover of oxygen to the cathodic electroplate. At first the cathodic titanium plate had considerably less oxygen than was initially in the anode, but continued operation without changing the electrolyte caused this improvement in purity to decrease until it reached an equilibrium level. Without being bound by the proposed theory, it is believed that the carryover of oxygen is directly due to the solubility of some combined form of oxygen in the electrolyte and to the occlusion and reaction, or either of these, between the dissolved oxygen and the titanium plate on the cathode. Thus the chemical characteristics of the electrolyte are a major factor in the carryover of oxygen from the anode to the cathode. The electrolyte should preferably, but not necessarily, be such that combined oxygen is substantially insoluble therein. For this reason anhydrous magnesium chloride is preferred for the electrolyte because oxygen compounds introduced from the titanium anode are sparingly soluble in it. The improvement attained in the oxygen content of the plate without positive deoxygenation may be attributed to insolubility of oxygen in the magnesium chloride electrolyte. As pointed out in application S.N. 414,899, the

soluble anode process for electroplating titanium on a suitable basis metal from a magnesium chloride electrolyte employs low cathode current density, namely less than 200 amps. per square foot, preferably 5-50 amps. per square foot, and elevated temperatures, preferably above the alpha-beta transition point of titanium. However, positive deoxygenation of the electrolyte does not depend on specific electrolytes; accordingly any electrolyte suitable for electroplating of titanium, in massive form, on a cathode, can be utilized in the titanium purification process of the present invention.

There are several methods of deoxygenating the electrolyte, both chemical and electrical. Typical chemical methods are purification or volatilization of the oxygen compounds. A specific example of chemical deoxygenation is introduction of dry hydrogen or chlorine, or more preferably HCl gas into the electrolyte suitably near the anode. The HCl reacts with the metal oxide toproduce H 0 and the corresponding chloride. At the temperature of the fused electrolyte, H O would be volatilized and removed from above the electrolyte surface with unreacted HCl. If desired, the HCl could be diluted with an inert gas such as helium or argon.

A preferred mode of deoxygenating the electrolyte is by electrolytic methods. Combined oxygen is ordinarily anionic and therefore anophoretic. Taking advantage of this characteristic, an electrolyte may be deoxygenated by an electrolysis involving an insoluble anode such as graphite. Any oxygen liberated at this anode would combine with the carbon to form volatile CO or CO In a preferred embodiment of the purification cell there would be three electrodes, a soluble anode of oxygencontaminated titanium, an insoluble anode, e.g. carbon, and a suitable cathode on which to electrodeposit the titanium. An electrolyte from which titanium can be electroplated is essential. Thus, for example, magnesium chloride alone or in admixture with non-interfering halides, e.g., a minor percentage of sodium chloride, will serve as electrolyte. All three electrodes may be operated continuously, or the insoluble anode may be operated intermittently. Other operating techniques such as will suggest themselves to those skilled in the art are also contemplated.

The following examples are presented to illustrate the practice of this invention.

Example 1.-Dry HCl gas is passed into a cell wherein a titanium anode containing approximately 9% oxygen is being plated onto an iron cathode using anhydrous MgCl as the electrolyte. The cathode titanium plate without positive deoxygenation contains approximately 7% oxygen. When the stream of HCl gas is passed throggh the electrolyte the oxygen content of the cathode iS 5 0.

Example 2.Using the same anode, cathode, electrolyte, and plating conditions, where without positive deoxygenation the cathode titanium plate contains 7% oxygen, an auxiliary carbon anode is introduced into the system to take part of the anode current. The oxygen content is again reduced to 5%. Such free magnesium as is liberated at the cathode does not interfere with the plating, and can be removed from the system as necessary.

Example 3.-Using the same cathode, electrolyte, and plating conditions and an anode of titanium scrap metal containing approximately 2% oxygen, without positive deoxygenation, the cathode plate contains 1 /2% oxygen. An auxiliary carbon anode introduced into the cell causes an oxygen reduction in the titanium plate on the cathode to a level less than /2 Zirconium is so closely allied to titanium that it has been called a non-identical twin of titanium. It, too, may be plated under the same conditions as titanium,

-- aesaeoa H and its purification under the conditions herein above delineated for titanium is expressly contemplated as falling within the scope of this invention.

What is claimed is:

H 1. A process for deoxygenating a metal selected from the group consisting of titanium and zirconium which comprises: anodically dissolving an oxygen contaminated anode formed from said metal into an electrolyte essentially consisting of molten magnesium chloride, said anode having less than 10% oxygen therein, whereby metal and oxygen dissolve into the electrolyte in chemically combined forms; removing the combined oxygen from the electrolyte by conversion of the oxygen into a gasiform product which escapes from the electrolyte; v

removing the volau'lized gasiform product from above the surface of said electrolyte; and simultaneously continuously plating said metal out in massive form at the cathode.

2. The process of claim 1 wherein the combined oxygen is removed from the molten magnesium chloride electrolyte by passing current through an auxiliary anode made of carbon into said electrolyte whereby the combined oxygen is transformed into gasiform products at said auxiliary carbon anode as a consequence of the overall electrolytic transfer of metal from the metallic anode to the cathode.

3. A process for deoxygenating a metal selected from the group consisting of titanium and zirconium which comprises: anodically dissolving an oxygen contaminated anode formed from said metal intoian electrolyte essentially consisting of molten magnesium chloride, said anode having less than 10% oxygen therein, whereby metal and oxygen dissolve into the electrolyte in chemically combined forms; removing the combined oxygen from the electrolyte by passing a stream of dry HCl gas through the electrolyte thereby converting the oxygen into a gasiforrn product which escapes from the electrolyte; removing the volatilized gasiform product from above the surface of said electrolyte; and simultaneously continuously plating said metal out in massive form at the cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,414,831 McNitt Ian. 28, 1947 2,731,402 Topinka et al. Jan. 17, 1956 2,734,856 Schultz et al Feb. 14, 1956 2,782,156 Raynes Feb. 19, 1957 FOREIGN PATENTS 1,064,893 France Dec. 30, 1953 170,508 Switzerland Sept. 17, 1934 OTHER REFERENCES The Production of Zirconium by Fused Salt Electrolysis, Atomic Energy Commission Report NYO-3117, pub. Jan. 1, 1952, pages 1-8. 

1. A PROCESS FOR DEOXYGENATING A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM WHICH COMPRISES: ANODICALLY DISSOLVING AN OXYGEN CONTAMINATED ANODE FORMED FROM SAID METAL INTO AN ELECTROLYTE ESSENTIALLY CONSISTING OF MOLTEN MAGNESIUM CHLORIDE, SAID ANODE HAVING LESS THEN 10% OXYGEN THEREIN, WHEREBY METAL AND OXYGEN DISSOLVE INTO THE ELECTROLYTE IN CHEMICALLY COMBINED FORMS; REMOVING THE COMBINED OXYGEN FROM THE ELECTROLYTE BY CONVERSION OF THE OXYGEN INTO A GASIFORM PRODUCT WHICH ESCAPES FROM THE ELECTROLYTE; REMOVING THE VOLATILIZED GASIFORM PRODUCT FROM ABOVE THE SURFACE OF SAID ELECTROLYTE; AND SIMULTANEOUSLY CONTINUOUSLY PLATING SAID METAL OUT IT MASSIVE FORM AT THE CATHODE. 